What I don't understand is why Mr Chicken sometimes repeats the offer for the same price at checkin. It happened to me today on ORD-DEN-OAK - I had upgraded the 777 ORD-DEN but was content with 8D on DEN-OAK. Mr Chicken asked me if I'd like to pay $130 to upgrade.

Why would I pay $130 to upgrade if I didn't want to use 2 500-milers to upgrade??